The objective of this project is to define the initial, intra-cellular events of steroid hormone action. Synthetic glucocorticoid derivatives, some of which could react to form covalently labelled receptors via affinity labelling, are being used with glucocorticoid-responsive rat hepatoma tissue culture cells to examine: (1) steroid-receptor binding site interactions; (2) the effects of steroid binding on receptor conformation; (3) the nature of "activation" of receptor-steroid complexes; (4) the nuclear binding of activated receptor-steroid complexes; and (5) receptor homology in closely related cell lines. A novel group of potential affinity labelling steroids, which may yield a functionally active, covalently labelled receptor, appear very promising. Fluorescence spectroscopy represents another technique for examining these interactions. For this reason, we have investigated the fluorogenic reaction of o-phthalaldehyde and Beta mercaptoethanol with primary amines and defined some of the chemical and fluorescence properties of the previously unknown isoindole products.